Centrifugal separator



.Murch 17, 1970 J, MULLER ETAL 3, 501001 GENTRIFUGAL SEPARATOR F1nd Snpt 16, 1968 INVENTORS Unted States Patent O 3,501001 CENTRIFUGAL SEPARATOR Jii Miiller and Rudolf Kmeco, Litovel, Czechoslovakra, assignors to Papcel Strojirny Pro Prumysl Celulosy a Papiru, uarodni podnik, Litovel, Czechoslovakra Filed Sept. 16, 1968, Set. No. 759,874 Claims priority, application Czechoslovakia, Sept. 22, 1967, 6,747/67 Int. Cl. Bld 21/06, B03d 1/14 U.S. C1. 209-211 9 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE DISCLOSURE This invention relates to papermaking equiprnent, and particularly to a centrifugal separator for purifying paper stock.

When paper stock is prepared trom rags or waste paper, it usually contains iron particles such as clips and staples and other particulate contaminants heavier than the suspended fibers. It is common practice to install a centrifugal separator between the regulating box and the screens on the paper machine. The centrifugal force may be created by an external pump whch forces the stock against suitably arranged deflecting surfaces in the separator casing. When stock of high consistency, three percent or more, is to be handled, separators equipped with a driven rotor in the casin g are more eiiective.

While the known separators with driven rotors constitute an important advance in the purification of high consistency stock, they are sensitive to changes in process variables. If the pressure or the velocity of the feed varies relatively slightly from the values for which the known separator is designed, its effectiveness decreases and heavy contaminants reacl1 the screens. The known separators are particularly sensitive to temporary increases in stock flow rate, and to pressure changes whch cause expansion and contraction of the air bubbles unavoidably present in the stock.

The object of the invention is the provision of a centrifugal separator for purification of paper stock which is 1ess sensitive to relatively small variatons in operating conditions than the known devices, and delivers paper stock of uniformly high purity.

SUMMARY OF THE INVENTION The invention is based on the known separator type in which the cavity of the separator casing is of circular cross section about practically the entire length of the normally vertical casing axis. A feed conduit admits paper stock to the upper end portion of the cavity through an orifice which is directed tangentially relative to the casing axis. A rotor is arranged in the upper end portion and a collector chamber gathers the heavy impurities at the bottom of the casing. A discharge conduit for purified paper has its orifice upwardly spaced from the collector chamber. The orifice intersects the casing axis and is axially directed against the bottom face of the rotor.

It has now been found that the performance of such a separator can be improved significantly by providing the bottom face of the rotor with a recess whose wall is a surface of revolution about the rotor axis, that is, the recess wall is of circular cross section about the axis. In its preferred form, the recess is of toroidal curvature, but recesses bounded by other surfaces of revolution are also etective at least to some extent.

The efliciency of the separator is further improved by shaping the rotor body and the rotor vanes according to one or more of the following features. The axial outer wall of the body, whch extends upwardly from the recessecl bottom face, should be of circular cross section about the separator axis, the two axially terminal portions of the wall Haring radially in a direction away from an axially central portion, and the lowermost part of the wall being substantially cylindrical and very narrow in an axial direction. Separation between the impurities and the fiber suspension is facilitate-d it the lowermost wall part and the recess in the bottom face define therebetween an annular edge portion of the latter even narrower than the cylindrical lowermost part of the axial wall.

The vanes are circumferentially disturbed on the rotor body in the usual manner. The upper portion of each vane extends in a helix of approximately uniform pitch and is at least partly coextensive in an axial direction with the orifice of the inlet conduit and the upper terminal portion of the axial wall on the rotor body. The lower portion of each vane is more nearly parallel to the rotor axis than the helix, and may be actually fiat in an axial plane.

The radially outer edges of the vanes jointly define an upwardly tapering concal surface during operation of the rotor, and the upper portion of the separator cavity is bounded by an upwardly tapering conical wall. The apex angle of the conical surface defined by the rotating vane edges is smaller than the apeX angle of the cone defined by the last mentioned wall.

Other features, additional objects, and many of the attendant advantages of this invention will readily be appreciated as the Same becornes better understood by reference to the following detailed description When consdered in connection with the appended drawing.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 shows a centrifugal separator of the invention in elevation, and partly in section on its vertical axis; and

FIG. 2 shows the rotor body of the separator and associated elements in axial, elevational section on a larger sca e.

DESCRIPTION OF THE PREFERRED EMBODIMENT Refernng now to the drawing, and initially to FIG. 1, there is seen a centrifugal separator whose sheet metal casing has a long, frustoconical, upwardly flaring bottom portion 1 connected by a short, cylindrcal section to an upwardly tapering, frustoconical upper portion 3 of intermedate axial length. An inlet conduit 4 communicates with the cavity in the upper casing portion by an orifice, obscured in the drawing by other elements, and directed tangentially into the cavity relative to the separator axis, as is well known in itself.

The radial top wall 5 of the casing provides a hearing, n0t shown in detail, for a vertical, coaxial drive shaft 6 from which the body portion 7 of a rotor is suspended in the upper end portion 3. The shaft 6 is driven by a nonillustrated motor in a conventional manner during operation of the separator.

As is better seen in FIG. 2, the rotor body 7 has the shape of an hour-glass, and flares frustoconically from a centra], narrow waist toward the two axial ends. The lowermost part of the body 7 is cylinclrical, but the axial idth of the cylindrcal wall 8 is less than one quarter of s radius. Whereas the two concal portions of the outer, xial body wall are axially coextensive with the conical all in the casing porton 3, the cylindrcal wall porton is coextensive in an axial direction with a part of the entral casing porton 2.

The radial bottom face 9 has a recess lwhose wall is surface of rotation similar to a porton of a torus. The tter wall and the cylindrcal lowermost porton 8 of the uter axial wall of the rotor body 7 meet at a small acute ngle to define an annular knife edge porton of the botm face 9. The wall of the recess forrns a downwardly irected, pointed projection in the center of the recess 10, nd extends in a circular are of almost 180 in each plane 1rough the rotor axis from the aforementioned knife dge to the point of central projection.

As is shown in FIG. 1 only, the rotor body 7 carries )UI' sheet metal vanes 11 which are equiangularly offset n the axial wall of the rotor body 7. An upper part of ach vane 11 extends in approximately 0ne turn of a helix f approximately uniform pitch about the separator axis nd is axially coextensive with the non-illustrated orifice f the inlet conduit 4 as is obvious from the location of 1e conduit, as seen in FIG. 1. The pitch of each helix 1creases sharply in a downward direction after one turn 3 that the lowermost porton of the vane is parallel or early parallel to the rotor axis.

As is indicated in FIG. 2, the radially outer edges 12 of ie rotor vanes 11 define a frustoconical surface 13 dur- 1g rotation of the rotor body 7. The apex angle of the onical surface 13 is smaller than the corresponding angle f the casing porton 3.

A discharge conduit 14 is partly coaxial with the rotor asing. Its upwardly directed circular orifice 15 thus interects the casing axis and is coaxially aligned with the entral projection in the recess The diameter of the rifice is approxirnately one third of the diameter f the recess 10, and the orifice is closely adjacent to the ottom face 9 in a downward direction, the axial spacing f the orifice from the bottom face 9 being but a small raction of the diameter of either. The conduit 14 down- 1ardly extends into a collector chamber 16 at the bottom f the separator casing and radially outward from the hamber. Its terminal flange 17 is normally connected to 1e papermaking machine.

A gate valve 18 may separate the chamber 16 from subjacent lock 19 which is usually closed in a down- 1ard direction by another gate valve 20. Washout fittings 1, 22 permit rinsing water to be introduced into the ook 19 or the chamber 16, the control valves in the water upply having been omitted for the sake of clarity.

The separator described above is operated as follows:

With the valves 18, 20 closed, the casing is filled with vater from the fitting 22, and the non-illustrated drive motor for the shaft 6 is started. Conta-minated paper tock is fed from a regulator box or other source through he inlet conduit 4 into the upper casing porton 3. The tock is driven mainly in an axially downward direction y the helical portions of the vanes 11, and is imparted predominantly circumferential and radially outward novement by the lower axial vane portions and by the entrifugal forces generated thereby. An outer vortex of ncoming stock develops along the casing walls and the pirals downward. The heavier contaminant particles are lriven toward the casing wall and move downward along he same toward the chamber 16 while the lighter fibers ravel with the carrier liquid downward, and then upward n an inner or central vortex about the conduit 14.

The preferred shapes of the rotor body 7, of the casing ortion 3, and of the vanes 11 enhance the formation of he descending vortex and its separating etect. The antular gap between the body porton 7 and the casing wall increases in a downward direction over the axial dimen ion of the orifice in the inlet conduit 4, thereby minimizng turbulence at the stock inlet, and favorng axially downward flow under the acton of the helical vane portions. As the lower porton of the body 7 flares downward, it assists the vanes 11 in driving the stock radially outward, and the axial flow velocity is decreased by the widening of the annular gap between the vane edges 12 and the less steeply inclined casing wall 3. Separation of the outer vortex from the axial wall of the body 7 with out excessive energy losses due to turbulence is made possible by the narrow cylindrcal wall porton 8 at the lowermost part of the body 7, thereby also preventing excessive mixing of the descending outer vortex with the ascending inner vortex.

Enough water is admitted during separator operation through the fitting 22 to rinse most adhering fibers from the falling impurities and to return the fibers to the ascending centra] vortex. The upward flow of the inner vortex is reversed, and the purified stock is drected downward and toward the axis into the orifice 15 by the approximately toroidal wall of the recess 10. The edge ofthe bottom face 9 is beneficial in separating the two vortexes which do not mix over a wide range of varying operating conditions, particularly variations in the flow rate and pressure of the incoming stock.

The collected impurities may be removed from the separator casing through the lock 19 without interruptng the operation of the apparatus by sequentially opening and closing the Valves 18, 20 at the two ends of the lock 19 in an obvious manner. Residual fibers may be washed from the impurties in the lock 19 by means of water admitted through the fitting 21 and returned to the inner vortex through the open valve 18.

We claim:

1. In a centrifugal separator for removing heavy impurities trom paper stock, the separator having a casing substantially enclosing a cavity of substantially circular cross secton about a normally vertically extending axis and being axially elongated; a feed conduit for admitting paper stock to upper end porton of said cavity and having an orifice in said end porton directed tangenta ly relative to said axis; a rotor mounted in said end porton for rotation about said axis; a collector chamber for said impurities at the bottom of said cavity; and a discharge conduit for purified paper stock having an orifice upwardly spaced trom said chamber, said rotor having a bottom face, and said orifice intersecting said axis and axially drected toward said bottom face, the improvement in the rotor which comprises:

(a) said rotor having a body porton carrying said bottom face and having an axial outer wall extending upwardly from said bottom face; and

(b) said bottom face being formed with a recess having a wall of circular cross secton about said axis.

2. In a separator as set forth in claim 1 said wall being of circular cross secton about said axis and having an axially central porton and two axially terminal portions radially flaring in a direction away from said central porton.

3. In a separator as set forth in claim 2, the lowermost part of said axial wall being substantially cylindrcal and of an axial width substantially smaller than the radius thereof.

4. In a separator as set forth in claim 3, said lowermost part and said recess defining therebetween an annular edge porton of said bottom face, the radial width of said edge porton being substantially smaller than said axial width of said lowermost part.

5. In a separator as set forth in claim 2, a plurality of vanes circumferentially distributed on said axial wall, each vane having an upper porton extending about said axis in a helix of approximately uniform pitch and a lower porton more nearly parallel to said axis than said helix.

6. In a separator as set forth in claim 5, said helix being at least partly axially coextensivc with the upper axally terminal porton of sad axal wa1l and with sad orfice of sad nlet conduit.

7. In a separator as set forth in claim 6, sad vanes having respectve radially outer edges jointly defining an upwardly tapering conical surface about sad axs during rotation of sad rotor, sad upper porton of sad cavity beng bounded by an upwardly tapering wal] of sad casng of c0nical shape about sad axis, the apex angle of the conical surface defined by sad edges being smaller than the apex angle of the cone defined by sad upwardly taperng wa1l.

8. In a separator as set forth in claim 1, sad recess being of substantially torodal curvature.

9. In a separator as set forth in claim 8, the axial dstance between sad bottom face and sad orfice of the discharge condut being substantially smaller than the greatest dimension of sad orfice perpendicular to sad ax1s.

References Cited UNITED STATES PATENTS 2,787,374 4/1957 Krebs 209211 2,975,896 3/1961 Hirsch 209-211 3,288,300 11/1966 Bouchllon 209-211 XR FOREIGN PATENTS 877,628 9/ 1961 Great Britain. 971,939 10/ 1964 Great Britain.

FRANK W. LU'IIER, Prmary Examner U.S. C1. X.R. 110-512 

